The present invention relates to a bonding material for a honeycomb structure and a honeycomb structure utilizing the bonding material. Particularly, it relates to a bonding material for manufacturing a honeycomb structure comprising a bonded honeycomb segment article in which the mutual bonding surfaces of a plurality of honeycomb segments are integrally bonded via bonding material layers and an outer peripheral coat layer which coats the outer peripheral surface of the bonded honeycomb segment article and having a structure in which a plurality of cells as through channels of a fluid are arranged in parallel with one another in a central axis direction, and it also relates to a honeycomb structure utilizing the bonding material. More particularly, it relates to a bonding material for a honeycomb structure preferably usable for a support for catalyst utilizing a catalytic function in an internal combustion engine, a boiler, a chemical reaction device, a reforming unit for a fuel cell or the like or for a filter for collecting fine particles in an exhaust gas or the like, and it also relates to a honeycomb structure manufactured by using the bonding material. Further particularly, it relates to a bonding material for a honeycomb structure, which has, for example, a large size but in which a plurality of honeycomb segments are securely bonded to one another, and a honeycomb structure.
A honeycomb structure made of a ceramic material is used for a support for catalyst utilizing a catalytic function in an internal combustion engine, a boiler, a chemical reaction device, a reforming unit for a fuel cell or the like or especially for a filter (hereinafter referred to as the DPF) for collecting diesel fine particles or the like.
In this type of ceramic honeycomb structure, a plurality of porous honeycomb segments having a large number of through pores partitioned by partition walls and extending in an axial direction are bound via adhesive layers to construct the structure (e.g., see Patent Document 1). That is, the ceramic honeycomb structure has a constitution in which the porous honeycomb segments having a square post-like shape are combined in rows and bonded to one another via the adhesive layers. At this time, after interposing the adhesive layer between the adhering surfaces of the porous honeycomb segments, the honeycomb segments are bonded while applying a pressing force thereto.
As a bonding material for bonding the honeycomb segments, silicon carbide powder has been suggested, and it has been pointed out the“silicon carbide powder has particle diameters of 0.01 to 100 μm, preferably 0.1 to 15 μm, more preferably 0.1 to 10 μm. This reason is that if the particle diameters exceed 100 μm, a adhesion force (the strength) and a heat conductivity are decreased. On the other hand, if the particle diameters are less than 0.01 cost increase is incurred” (e.g., see Patent Document 2).
Moreover, it is suggested in Patent Document 2 that ceramic member are integrally adhered via a seal material and that inorganic powder or whiskers of at least one or more selected from the group consisting of silicon carbide, silicon nitride and boron nitride are used as inorganic particles. However, in the method of Patent Document 2, it has been difficult to achieve a balance between the improvement of the flow properties as well as water-holding properties of a bonding material slurry and the increase of the heat conductivity. When the inorganic particles of the bonding material slurry are coarse, a grain boundary having a thermal resistance decreases, and hence the heat conductivity can be increased. However, when the inorganic particles are coarse, the flow properties of the bonding material slurry are remarkably impaired, and hence it is difficult to completely fill a bonded part with the slurry, thereby causing the decrease of the bonding strength. Moreover, when the grain size distribution of the inorganic particles is coarse, the surface of the slurry immediately dries, which disturbs the interface adherence of the bonded part sometimes.
[Patent Document 1] JP-A-2000-7455
[Patent Document 2] JP-A-08-28246